The long-term goal of this research is to learn more about the structure and function of herpesvirus proteins, and translate that information to new diagnostic, preventive, and therapeutic strategies for dealing with CMV-related diseases of man. We use cytomegalovirus (CMV) as our model system because of its medical relevance to immunosuppresion resulting from AIDS, organ transplantation, and cancer chemotherapy, and to sexually transmitted diseases and birth defects. Additionally, there is a need to determine the molecular similarities and differences between herpes group viruses in order to understand their biological differences. Our more immediate objectives are to study the synthesis, structure, and function of specific viral proteins that are essential for virus replication, with a concentration on those involved in virus assembly. Our rationale for studying virus structure and assembly is that most aspects of virus replication are directly or indirectly coupled to the assembly process; therefore, it ultimately represents a major and largely untapped source of new targets for antivirals. The specific aims of the work proposed here are to uncover processes that modulate the very early and intermediate stages of CMV assembly. We will continue our studies of how the proteins of the capsid interact and why, and what modifications they undergo and how these govern the process of capsid formation and maturation. Our plans also include studying three of the tegument proteins that appear to be most closely associated with the capsid and which may anker other tegument or envelope proteins to the capsid, or perhaps help the capsid negotiate the nuclear membrane as it exits or target it after entry. We will apply a combination of biochemical, cryo-EM/imaging, and genetic experiments to bear on these questions, including (i) use of a recently developed in vitro binding system to study capsid/tegument interactions, and (ii) use of the HCMV-bacterial artificial chromosome system to produce mutant viruses.